Genetic and phenotypic parameter estimates for scrotal circumference and semen traits in young beef bulls

Estimated in this study were heritabilities and genetic and phenotypic correlations involving scrotal circumference (SC), percent live sperm, sperm number, sperm concentration, sperm motility, and an overall measure of a bull's potential breeding efficiency. Potential breeding efficiency is a composite trait based on a consideration of sperm concentration, sperm motility, sperm morphology and scrotal circumference. Data used were from three sources. Records on 863 Angus, 753 Polled Hereford, and 302 Simmental bulls were made available through the Missouri Performance-Tested Bull Sale and records on 1169 Polled Hereford bulls came from the American Polled Hereford Association. Information from these first two data sets were used to estimate heritability of scrotal circumference. The third data set was provided by Nichols Farms of Bridgewater, Iowa, and included information from the records of 465 yearling Polled Hereford and 264 yearling Simmental bulls. This latter data set was used to estimate all of the above mentioned parameters. Each data set was kept separately for the purpose of statistical analysis. Parameters were estimated using components from paternal half-sib analysis of variance and covariance. Pooled estimates of heritability for SC, sperm concentration, sperm motility, percent live sperm, sperm number and potential breeding efficiency were 0.51 +/- 0.09, 0.20 +/- 0.13, 0.11 +/- 0.12, 0.00, 0.19 +/- 0.14 and 0.13 +/- 0.12, respectively. Phenotypic correlations involving the six traits were very consistent for the two breeds. Combined across breeds their values ranged from 0.47 for SC and percent live sperm to 0.96 for sperm concentration and potential breeding efficiency. Corresponding genetic correlations were generally positive and high and ranged from 0.65 for SC and sperm motility to 1.14 for sperm number and potential breeding efficiency.     

Proteins of the accessory sex glands associated with the oocyte-penetrating capacity of cauda epididymal sperm from holstein bulls of documented fertility

We previously reported that accessory sex gland fluid (AGF) from high fertility (HF) bulls influenced the oocyte-penetrating capacity of cauda epididymal sperm from low fertility (LF) bulls, based on in vitro fertilization (IVF) assays. The present study determined if AGF proteins were associated with these effects. Nineteen IVF assays with 12 bulls were grouped as follows. Group I (n = 8): assays where sperm from LF bulls exposed to AGF from HF bulls had greater oocyte penetration than exposed to homologous AGF. Group II (n = 7): sperm from LF bulls to AGF from HF bulls versus homologous AGF showed no significant differences. Group III (n = 4): sperm from LF bulls treated with homologous AGF had greater fertility than sperm treated with AGF from HF bulls. Sire fertility was based on nonreturn rates (NNR) and AGF collected by artificial vagina from bulls with cannulated vasa deferentia. Two-dimensional SDS-PAGE maps of AGF were analyzed by PDQuest and proteins identified by tandem mass spectrometry and Western blots. Differences in spot intensity between AGF of HF and LF bulls were compared across groups of IVF assays (P < 0.05). The expression of BSP A1/A2 and A3, BSP 30 kDa, clusterin, albumin, phospholipase A(2) (PLA(2)), and osteopontin was greater in the AGF of HF bulls in Group I as compared to Groups II and III. Conversely, there was less nucleobindin in the AGF of HF bulls in Group I than in Groups II and III. This is the first report of nucleobindin (58 kDa/pI 5.6) in male reproductive fluids, using both immunoblots and mass spectrometry. Thus, the effect of AGF from HF bulls on epididymal sperm is likely the result of specific proteins expressed in the AGF.     

Growth hormone gene polymorphism and reproductive performance of AI bulls

Relationships between the growth hormone gene RFLP polymorphism and bull sperm characteristics were the objects of the present study. DNA was extracted from blood or sperm samples collected from 113 AI bulls and submitted for polymerase chain reaction (PCR) followed by digestion with Alu I restriction enzyme. The bGH genotypes were visualized on 10% polyacrylamide gel. The analyzed population of AI bulls consisted of dairy (Holstein Fresian [HF] crossbred [HF x Polish Black and White]) and beef breeds (Limousine, Charolaise, Piemontese, Angus and Hereford). The frequency of the Leu allele was 0.86 among dairy bulls and 0.38 in beef bulls (0.14 and 0.62 for the Val allele, respectively). Eight sperm characteristics and Day 60 non-return rates (NRR) were analyzed. The 3 genotype groups (LL, VV and LV) and the effect of production type (dairy or beef) on sperm characteristics were considered. None of the traits showed significant variability in relation to the bGH genotype, although a tendency was observed for LL bulls to have a lower ejaculate volume and VV bulls higher NRR. Moreover some statistically significant associations with production type were noticed: beef bulls were superior in sperm concentration and non-return rate, whereas dairy bulls excelled in individual fresh sperm motility.     

Pregnancy rate in cows and heifers bred to bulls selected for semen quality

A two-year study was conducted to compare fertility in cows or heifers bred to either an unselected group of bulls or bulls selected for semen quality. An improvement of 5% in pregnancy rate was found the first year in 591 cows bred to bulls having 80% or more normal sperm, compared to the 656 cows bred to a group of bulls representative of the original population (original group). A similar difference in pregnancy rate was noted the second year between 1179 heifers bred to the original group of bulls and the 522 heifers bred to bulls having 80% or more normal sperm and the 769 heifers bred to bulls with 70% or more normal sperm.     

Effects of scrotal insulation on sperm production,semen quality,and testicular echotexture in Bos indicus and Bos indicus x Bos taurus bulls

The objectives of the present study were to evaluate the effects of scrotal insulation on sperm production, semen quality, and testicular echotexture in Bos indicus and Bos indicus x Bos taurus crossbred bulls. In one experiment, B. indicus bulls (n=12) were allocated to control and whole-scrotum insulation groups, while in a second experiment, crossbred bulls (n=21) were allocated into control, whole-scrotum, and scrotal-neck insulation groups. Insulation was applied for 4 days (start of insulation = Day 0) and semen collection and testicular ultrasonographic examinations were performed twice weekly until Day 35. Sperm concentration and total sperm output during the post-insulation period were greater in control groups, but significant differences were observed only in B. indicus bulls. Overall, sperm motility in scrotal-insulated B. indicus bulls was lower (P<0.05) than in the control group. After whole-scrotum insulation in crossbred bulls, sperm motility was lower (P<0.05) than pre-insulation levels between Days 21 and 31, and lower than control levels on Day 24. The proportion of normal sperm after whole-scrotum insulation was lower than pre-insulation and control values from Day 11 to the end of the experiment in B. indicus bulls (P<0.05 from Days 14 to 21 and on Day 27), and from Days 14 to 25 in crossbred bulls (P<0.05 on Days 14 and 18). Insulation of the scrotal neck in crossbred bulls did not significantly affect semen quality. Loose sperm heads (Day 11), midpiece defects (Days 11 and 14), and acrosome defects (Days 27 and 31) increased (P<0.05) in insulated B. indicus bulls, while proximal cytoplasmic droplets (Days 14, 18 and 27 in B. indicus; Days 24 and 27 in crossbred bulls) and sperm vacuoles (Days 18 and 21 in B. indicus; Day 18 in crossbred bulls) increased (P<0.05) in whole-scrotum insulation groups in both experiments. There was considerable variation among bulls in the incidence of specific sperm defects. The timing of appearance of sperm defects after insulation provided insights into the pathogenesis of specific abnormalities. Neither whole-scrotum nor scrotal-neck insulation affected testicular echotexture in either experiment. In conclusion, whole-scrotum insulation resulted in decreased sperm production and semen quality in B. indicus and B. indicus x B. taurus bulls, but those changes were not associated with changes in testicular echotexture.     

Associations of scrotal circumference with semen traits in young beef bulls

Associations of percent live sperm, sperm number, sperm concentration, sperm motility, and potential breeding efficiency score with scrotal circumference were studied using data from the records of 465 Polled Hereford and 264 Simmental bulls. Data were subdivided by breed and within breed into three groups according to scrotal circumference (SC) size. Group I bulls had SC measurements <32 cm. Group II included bulls with SC measurements between 32 cm and the mean measurement of the breed (i.e., 35 cm for Polled Hereford and 38 cm for Simmentals). Group III was comprised of bulls with SC values above their respective breed averages. Age and body weight differences were also evaluated in the three groups. Average age differences among bulls in the three groups differed by not more than nine days in the two breeds. Average body weight differences among the three groups were statistically significant (P<0.05) with the maximum difference between any two groups within breed being 80 pounds. Average differences in percent live sperm and sperm number were greater (P<0.05) in Groups II and III than in Group I. For sperm concentration ratings, sperm motility ratings and potential breeding efficiency score, and for both breeds, Group I had a significantly lower (P<0.05) number of bulls classified satisfactory and a significantly greater (P<0.05) number of bulls classified unsatisfactory than did groups II and III.     

Use of chromomycin A3 staining in bovine sperm cells for detection of protamine deficiency

Sperm chromatin integrity is essential for accurate transmission of male genetic information, and normal sperm chromatin structure is important for fertilization. Protamine is a nuclear protein that plays a key role in sperm DNA integrity, because it is responsible for sperm DNA stability and packing until the paternal genome is delivered into the oocyte during fertilization. Our aim was to investigate protamine deficiency in sperm cells of Bos indicus bulls (Nelore) using chromomycin A₃ (CMA₃) staining. Frozen semen from 14 bulls were thawed, then fixed in Carnoy's solution. Smears were prepared and analyzed by microscopy. As a positive control of CMA₃ staining, sperm from one bull was subjected to deprotamination of nuclei. The percentage of CMA₃-positive bovine sperm did not vary among batches. Only two bulls showed a higher percentage of CMA₃-positive sperm cells compared to the others. CMA₃ is a simple and useful tool for detecting sperm protamine deficiency in bulls.     

Sperm accumulation in the ampullae and cauda epididymides of bulls

Bulls that appear to have an abnormality of sperm transport accumulate large numbers of senescent sperm in the excurrent ducts of the reproductive tract. Six bulls that accumulated sperm were used to determine the number of physiological ejaculations required to deplete accumulated senescent sperm, semen traits during depletion, the period of time to re-accumulate senescent sperm after depletion, the sites of sperm accumulation, and the effect of sperm accumulation on fertility during natural service. Semen was collected from three bulls (HH, PH1, and CH1) three times daily using internal artificial vaginas placed in cows in estrus. These bulls started to produce semen with >or=70% morphologically normal sperm on the third, fifth, and seventh day, respectively. The percentage of live sperm increased from 5% to 68%, 5% to 63%, and 18% to 68% in HH, PH1, and CH1, respectively. Two weeks later the same bulls were electroejaculated every second day for five electroejaculations to deplete stores of senescent sperm. Each time, electroejaculation was continued until the semen produced had a dilute appearance. The three bulls re-accumulated senescent sperm after 1 month of sexual rest. After re-accumulation of senescent sperm, the total volumes of semen in both ampullae recovered at slaughter from HH, PH1, and CH1 were 5.0, 5.0, and 9.5 ml, respectively. The volumes of semen in ampullae recovered at slaughter from two control bulls (RA and CHC) were 1.7 and 1.9 ml, respectively. The number of sperm recovered from both cauda epididymides of HH, PH1, CH1, RA and CHC was 37.3x10(9), 23.3x10(9), 15.0x10(9), 6.9x10(9), and 7.4x10(9), respectively. Bull CH1 and a fourth bull (LM) that also accumulated sperm, started to produce semen with >or=70% morphologically normal sperm, and >or=60% progressively motile sperm on the third electroejaculation after depletion of senescent sperm by repeated electroejaculations. Pregnancy rates achieved by two bulls that accumulated senescent sperm (CH2 and PH2) were less (P<0.05) during the first week of a 21-day breeding period and there was a tendency for lesser pregnancy rates at the end of the breeding period when compared with two normal control bulls. The present study indicates that bulls that accumulate senescent sperm may achieve greater pregnancy rates approximately 1 week after beginning a period of frequent ejaculation. Re-accumulation of an increased percentage of senescent sperm would likely occur after 1 month of sexual rest.     

Testicular development and its relationship to semen production in Murrah buffalo bulls

The objectives of this study were to determine the relationship of age and body weight to testicular development and to establish norms for breeding soundness evaluations of Murrah buffalo bulls. Testicular measurements of 133 Murrah buffalo bulls of various ages were recorded with a caliper and a tape. Semen was collected twice a week for 5 weeks from groups of bulls which were 25-36 (n=17), 37-48 (n=16), 49-60 (n=14), of >60 (n=10) months of age. After examining volume, sperm concentration, and progressive motility semen was diluted in Tris-citric acid-egg yolk-fructose extender and frozen in 0.5 ml French straws. Testicular measurements of buffalo bulls were lower than those recorded for European breeds of cattle bulls. Nevertheless, like cattle bulls, scrotal circumference was highly correlated with other testicular measurements. Also, it had a significant positive relationship with semen volume and sperm concentration per ejaculate. Average sperm output per week in order of increasing age group was 15.3, 18.2, 19.8 and 23.6 x 10(9). Corresponding values for sperm output per week per gram of testis were 59.1, 45.8, 41.1, 36.2 x 10(6) indicating a reduction in spermatogenesis per unit of testis with advancing age. Compared to European breeds, daily sperm output in Murrah bulls was nearly 45% lower, presumably due to their nearly 40% lower scrotal circumference than Holstein bulls of the same age. These results indicate that in buffalo, as in cattle, scrotal circumference is a useful indicator of potential sperm output and may serve as an important criterion for selecting young bulls as AI sires.     

Effects of heparin and sperm concentration on cleavage and blastocyst development rates of bovine oocytes inseminated with flow cytometrically-sorted sperm

The objective was to determine the optimal concentration of heparin for sperm capacitation, as well as the optimal sperm concentration for in vitro fertilization using flow cytometrically-sorted sperm from individual bulls. A total of 5327 bovine oocytes and sperm from four bulls were examined. Oocytes from slaughterhouse ovaries were matured in TCM199 for 22-24 h. Flow cytometrically-sorted sperm as well as unsorted control sperm from the same bulls were cryopreserved. For sperm from each of the four bulls, oocytes were inseminated in a three-by-three factorial design plus one control group (three heparin concentrations: 0, 2, and 10 microg/ml and three sperm concentrations: 0.5 x 10(6), 1.5 x 10(6), and 4.5 x 10(6) ml(-1); 10 microg/ml of heparin and 1.5 x 10(6) ml(-1) of sperm were used for the unsorted control). Presumptive zygotes were cultured in chemically defined media, CDM-1 and CDM-2 for 52-54 h and 96 h, respectively. Samples of about 10 oocytes from each of the 10 treatment groups per replicate were fixed at 18-20 h after insemination to determine sperm pronuclei formation and polyspermy. Increased polyspermy resulted as heparin and sperm concentrations increased (P < 0.05). A higher rate of polyspermy was found in oocytes inseminated with unsorted control sperm compared with sorted sperm (P < 0.05). Sperm of one of four bulls tested required no heparin and lower concentration (0.5 x 10(6) ml(-1)) to obtain optimal cleavage and blastocyst rates while optimal parameters for another bull were higher heparin (10 microg/ml) and sperm concentrations (4.5 x 10(6) ml(-1)). Optimal parameters for the other two were intermediate levels of heparin and sperm. Sperm appeared to be partially capacitated during the flow cytometric-sorting process used for sex pre-determination. When heparin and sperm concentrations were optimized for individual bulls, blastocyst production per oocyte was similar for sorted and unsorted sperm for three of the four bulls studied.     

Characterization of seminal plasma proteins and sperm proteins in ejaculates from normospermic bulls and bulls with thermally-induced testicular degeneration

Semen was collected from 5 mature beef bulls by electroejaculation before, during, and after 20 days of scrotal insulation. Thermally-induced testicular degeneration was irreversible in 3 of the bulls. Analysis of sperm and seminal plasma polypeptides revealed that 15 to 30 sperm polypeptides and 25 to 30 seminal plasma polypeptides were indistinguishable between bulls prior to the insulation treatment. Changes in the sperm polypeptides pattern appeared as early as 2 days after the insulation treatment and persisted for at least 11 months in 2 of the bulls. In the spermatozoa, there was a detectable loss of 31, 34, 49 and 58 kDa polypeptides and an appearance of 6 to 8 new major polypeptides, ranging from 32 to 83 kDa. The 83 kDa polypeptide was most prominent in the 2 bulls that regained normal sperm motility and morphology following the insulation period. The post-insulation appearance of a seminal plasma polypeptide (circa 60 kDa) was also identified in these 2 bulls. Seminal plasma polypeptides remained qualitatively unaltered by the insulation treatment in the 3 bulls with irreversible testicular degeneration.     

Reversibility of the reproductive toxicity of gossypol in peripubertal bulls

Gossypol has been shown to impair sperm production in male ruminants. The purpose of this study was to determine if the adverse effects of gossypol on spermatogenesis in peripubertal bulls were reversible. Twenty-eight crossbred Angus bulls were allocated into treated and control groups at 11 months of age. For 8 weeks, treated bulls were fed a ration containing 8 mg of free gossypol per kilogram of body weight per day while control bulls were fed a soybean meal ration free of gossypol. At 28-days intervals, scrotal circumference was measured and semen collected to assess sperm motility and morphology. Seven control and seven treated animals were castrated 56 days after the start of the experiment and the testes were examined histologically. The remaining bulls were fed a gossypol-free diet for 210 days prior to castration. There were significant increases in primary and secondary sperm abnormalities in treated bulls 28 and 56 days after gossypol feeding. The number of sperm with proximal droplets was significantly higher in gossypol-treated bulls, suggesting testicular degeneration. There was no significant effect on the sperm motility, scrotal circumference, or histopathological characteristics of the testes. Four weeks after the end of gossypol feeding, primary and secondary abnormalities were still increased in gossypol-treated bulls, however in subsequent collection periods the percentage of abnormalities were similar between groups. At 210 days, there was no treatment effect on scrotal circumference, and histological characteristics of the testes were not different between groups. The deleterious effects of gossypol on the morphological characteristics of spermatozoa were reversible. Gossypol (8 mg/kg per day for 56 days) increased sperm abnormalities but the effects were reversible.     

The effects of feed restriction and realimentation on the growth and reproductive function of Bokoloji bulls

A group of Bokoloji bulls (n=36), consisting of 18 young bulls (12 to 18 mo old) and 18 old bulls (24 to 30 mo old) were used to study the effects of feed restriction and realimentation on reproductive function. The bulls were placed either on a low (L). medium (M) or high (H) plane of nutrition during the 3 treatment periods. At the low and medium feeding levels, the animals received approximately 25 and 45%, respectively, of the intake of the bulls on the high plane diet. All the bulls were fed a low (L) plane of nutrition for 90 d in the first treatment period. The 3 treatments were designated as LL, LM and LH for the mid-period, and as LLH, LMH and LHH for the final period, according to the prescribed level of feeding. Body measurements and scrotal circumference were taken for all bulls before slaughter. A total of 18 bulls was slaughtered at the end of the mid-period, while the remaining 18 bulls were slaughtered at the end of the final period. Testicular weights as well as gonadal and epididymal sperm reserves were determined. At the end of the mid period, the bulls on a high plane of nutrition had significantly (P<0.05) higher live weights and chest girths than bulls on the medium and low planes of nutrition. Gonadal sperm/spermatid reserves of 5.2 x 10(9) and epididymal sperm reserves of 2.4 x 10(9) in bulls on the high plane of nutrition were significantly (P<0.05) higher than the sperm reserves for the bulls on either the low or the medium plane of nutrition. At the end of the final period, ho significant differences existed among the LHH, LMH and LLH treatments in liveweight, chest girth, scrotal circumference and sperm reserves (P>0.05). It is concluded that bulls which have undergone feed restriction for 90 d are capable of regaining their body growth and reproductive function if such bulls are placed on an adequate plane of nutrition.     

Changes in the morphology of spermatozoa during their passage through the genital tract in dairy bulls with normal and impaired spermat ogenesis

An investigation was conducted on changes in sperm morphology along the excurrent duct of bulls. The study comprised 20 bulls with proven fertility and normal semen picture, and 10 bulls with pathologic semen. The morphology of spermatozoa was evaluated on ejaculates and on postslaughter collected contents from the excurrent duct. The incidence of pathologic sperm heads decreased along the duct in both groups of bulls. The main decrease generally occurred in caput epididymidis. In bulls with pathologic semen, the decrease continued in lower regions of epididymis and was deferens. The rate and pattern of sperm removal seem to primarily depend on the quality of spermatozoa entering the excurrent duct. The removal was clearly selective and is assumed to be associated with phagocytosis of spermatozoa mainly in the efferent ductules and proximal part of caput epididymis. Proximal cytoplasmic droplets were present on almost all sperm in the efferent ductules. The incidence decreased during passage along the genital tract. Migration of cytoplasmic droplets from a proximal to a distal position took place between regions C and D of the caput epididymidis. The incidence of middle-piece abnormalities decreased during passage along the genital tract, while the incidence of sperm tail abnormalities increased in the corpus and cauda epididymidis in all bulls.     

Variation in lipid profiles within semen compartments—the bovine model of aging

Semen lipid composition was examined in young and mature bulls. Given the specific roles of various semen compartments (i.e., seminal fluid, sperm head, and sperm tail) during fertilization, we hypothesized that altered fatty acid and cholesterol composition of a specific compartment might impair semen quality and sperm function. Semen samples were collected from five mature and five young Holstein Friesian bulls during the winter (December–January). Semen was evaluated by computerized sperm-quality analyzer for bulls and was centrifuged to separate the sperm from the seminal fluid. The sperm fraction was sonicated to separate its head and tail compartments. Cold extraction of lipids was performed, and fatty acids and cholesterol were identified and quantified by gas chromatography. Semen physiological features (concentration, motility, and progressive motility) did not differ between mature and young bulls. However, lipid composition within fractions varied between groups, with prominent impairments in the head compartment. In particular, the proportions of polyunsaturated fatty acids, omega-3 fatty acids, and docosahexaenoic acid in the intact sperm; seminal fluid; and sperm head were lower in semen collected from mature bulls than in that from young bulls. The finding suggests an age-differential absorption and/or metabolism through spermatogenesis. Reduced proportions of major fatty acids in mature bulls might reduce membrane fluidity, which in turn might affect the ability to undergo cryopreservation and/or oocyte-sperm fusion through fertilization.     

Sexual development in early- and late-maturing Bos indicus and Bos indicus x Bos taurus crossbred bulls in Brazil

Two experiments were conducted to evaluate sexual development in early- and late-maturing Nelore (Bos indicus) and Canchim (3/8 Bos indicus x 5/8 Bos taurus crossbred) bulls and to determine predictors of sexual precocity, and pubertal and maturity status. In Experiment 1, 12 Nelore bulls where examined from 300 to 900 days of age. Puberty was characterized by an ejaculate containing > or =50 million sperm with > or =10% motile sperm, and maturity by an ejaculate containing > or =70% morphologically normal sperm. In Experiment 2, 28 Canchim bulls where examined from 295 to 488 days of age and puberty was characterized by an ejaculate containing > or =30% motile sperm. In both experiments, bulls were classified as early- or late-maturing based on age at puberty. Early-maturing bulls were younger (P < 0.05) than late-maturing bulls at puberty (527 days versus 673 days in Experiment 1 and 360 days versus 461 days in Experiment 2) and at maturity (660 days versus 768 days in Experiment 1). In general, early-maturing bulls were heavier and had greater scrotal circumference (SC), testes, and testicular vascular cone diameter than late-maturing bulls during the experimental period. Scrotal circumference adjusted for 365 days of age was a good predictor of sexual precocity; minimum yearling SC of 19 and 24 cm for Nelore and Canchim bulls, respectively, had the best predictive values. Early-maturing bulls were lighter and had smaller SC at puberty than late-maturing bulls; therefore, sexual precocity was not related to the attainment of a threshold body weight or testicular size earlier, but to lower thresholds in early-maturing bulls. When predictors of pubertal status were evaluated, SC had the best sensitivity/specificity relationship in Nelore bulls, and high sensitivity and specificity in Canchim bulls. When predictors of sexual maturity were evaluated in Nelore bulls, age, weight, and SC had similar sensitivity, specificity, and predictive values. At puberty, approximately 60% of the sperm present in the ejaculate were morphologically defective. Changes in semen quality after puberty in Nelore bulls were characterized by increased motility and proportion of morphologically normal sperm, with a decrease in the proportion of major sperm defects. In conclusion, early-maturing bulls were more developed in the pre-pubertal period and attained puberty at earlier stages of body and testicular development than late-maturing bulls. Yearling SC could be used to select bulls for sexual precocity and SC was the best predictor of pubertal status. Age, weight, and SC were equally good predictors of sexual maturity in B. indicus bulls.     

Effects of environmental factors, age and genotype on sperm production and semen quality in Bos indicus and Bos taurus AI bulls in Brazil

The effects of ambient temperature and humidity, month, age and genotype on sperm production and semen quality in AI bulls in Brazil were evaluated. Data from two consecutive years were analyzed separately. Seven Bos indicus and 11 Bos taurus bulls from one artificial insemination (AI) center were evaluated in Year 1 and 24 B. indicus and 16 B. taurus bulls from three AI centers were evaluated in Year 2. Ambient temperature and humidity did not significantly affect sperm production and semen quality, probably because there was little variation in these variables. Month accounted for less than 2% of the variation in sperm production and semen quality. Increased bull age was associated with decreased sperm motility (P<0.10) and increased minor sperm defects (P<0.001) in Year 1. B. indicus bulls had greater (P<0.005) sperm concentration than B. taurus bulls in both years (1.7×10⁹/ml versus 1.2×10⁹/ml in Year 1 and 1.6×10⁹/ml versus 1.2×10⁹/ml in Year 2, respectively). Ejaculate volume was not significantly affected by genotype in Year 1 (6.6 ml versus 6.9 ml in B. indicus and B. taurus bulls, respectively), but B. indicus bulls had greater (P<0.05) total (11.4×10⁹ versus 8.2×10⁹) and viable (6.7×10⁹ versus 4.9×10⁹) numbers of spermatozoa in the ejaculate than B. taurus bulls. In Year 2, B. taurus bulls had greater (P<0.05) ejaculate volume than B. indicus bulls (8.2 ml versus 6.7 ml, respectively) and total and viable number of spermatozoa in the ejaculate were not significantly different between genotypes (10.3×10⁹ versus 9.1×10⁹ and 6.1×10⁹ versus 5.4×10⁹ in B. indicus and B. taurus bulls, respectively). Sperm motility was not significantly affected by genotype (mean, 59%). In Year 1, B. indicus bulls tended (P<0.10) to have more major sperm defects and had more (P<0.05) total sperm defects than B. taurus bulls (11.8% versus 8.7% and 13.6% versus 10.0%, respectively). In Year 2, B. indicus bulls tended (P<0.10) to have more total sperm defects than B. taurus bulls (16.2% versus 13.3%, respectively). In conclusion, neither ambient temperature and humidity nor month (season) significantly affected sperm production and semen quality. B. indicus bulls had significantly greater sperm concentration and B. taurus bulls had significantly fewer morphologically defective spermatozoa.     

Effect of age and genetic group on characteristics of the scrotum,testes and testicular vascular cones,and on sperm production and semen quality in AI bulls in Brazil

The objectives were to determine the effects of age and genetic group on characteristics of the scrotum, testes and testicular vascular cones (TVC), and on sperm production and semen quality in 107 Bos indicus, B. taurus and cross-bred bulls at three artificial insemination (AI) centers in Brazil. In addition, predictors of sperm production and semen quality were identified. In general, scrotal circumference (SC), scrotal shape score, scrotal neck perimeter, and testicular size (length, width and volume) increased (P < 0.05) with age. Although there were no significant differences among genetic groups for SC or testicular size, B. indicus bulls had the least pendulous scrotal shape, the shortest scrotal neck length, and the greatest scrotal neck perimeter (P < 0.05). Fat covering the TVC was thinner (P < 0.05) in bulls < or = 36 months of age and in B. taurus bulls than in older bulls and B. indicus bulls, respectively. Age and genetic group did not affect testicular ultrasonic echotexture. B. indicus bulls tended (P < 0.1) to have the lowest average scrotal surface temperature (SST). In general, ejaculate volume, total number of spermatozoa and number of viable spermatozoa increased (P < 0.05) with age. However, there was no significant effect of age on sperm concentration, motility, major and total defects. The proportion of spermatozoa with minor defects was highest (P < 0.05) in bulls 37-60 months of age. B. indicus bulls had higher (P < 0.01) sperm concentration, total number of spermatozoa and number of viable spermatozoa than B. taurus bulls, with intermediate values for cross-bred bulls. Increased sperm production was associated with increased testicular volume, SC, TVC fat cover, and SST top-to-bottom gradient. Decreased semen quality was associated with increased SC and bottom SST, and decreased scrotal shape, scrotal neck perimeter and vascular cone diameter. In summary, age and genetic group affected the characteristics of the scrotum, testes, and TVC, sperm production and semen quality. In addition, characteristics of the scrotum, testes and TVC were associated with sperm production and semen quality in bulls and could be assessed for breeding soundness evaluation.     

Effect of long-term immunization against inhibin on sperm output in bulls.

To determine the effect of neutralization of inhibin on sperm output, 12 Holstein bulls were paired by birth date and weight on Day 1 of age. Each bull was actively immunized against bovine inhibin alpha1-26 gly-tyr (bINH) conjugated to human alpha globulin (HAG, n = 6 bulls) or HAG alone (controls, n = 6) at 60 days of age; booster immunizations were administered at 90, 104, 124, 270, and 395 days of age. Body weights and scrotal circumferences were measured at the time of primary immunization and at 10 days after each booster. In addition, jugular blood was obtained at 60, 70, 100, 114, 134, 280, and 405 days of age, during the 3-wk sperm collection period, and during a 6-h blood-sampling period after sperm collection to determine bINH antibody titer and concentrations of FSH, LH, testosterone, and estradiol. Beginning at 405 days of age, sperm output was measured 3 days/wk for 3 wk with two successive ejaculates collected each day for a total of 18 ejaculates per bull. During Days 60-405 of age, the increase in titer of bINH antibodies, scrotal circumference, and serum concentration of FSH was greater (p < 0.01) for the bINH-immunized compared with control bulls. There were significant (p < 0.01) pair x treatment interactions for sperm output and serum FSH and LH concentrations. Specifically, bINH-immunized bulls for four of the six pairs had nearly 50% greater serum FSH concentrations and sperm output. For the remaining two pairs, sperm output was lower and FSH was either lower or only marginally higher in the bINH-immunized bulls compared with controls. Also, the control bulls for the two remaining pairs produced more sperm than all but one bINH-immunized bull, and had markedly higher serum LH concentrations than all other bulls. To summarize, enhancement of sperm output after immunization against inhibin depends on the subsequent increment in FSH concentrations. We conclude that inhibin suppresses spermatogenesis. Thus, methods to immunoneutralize inhibin may have merit as a therapeutic route to enhance sperm production in reproductively maturing bulls.